Over the last decade, a number of lower-extremity exoskeletons have been developed to assist human gait in various conditions. Some devices have been designed to assist impaired or able-bodied people, while others have been designed to make load carriage easier. Conventionally, these devices have consisted of rigid exoskeleton structures enabling high assistive torques to the wearer. However, rigid frames can restrict the natural movement of the wearer and may apply undesired forces when they are misaligned with the wearer's biological joints. Moreover, rigid devices may have large inertias particularly on distal areas, which can hinder the motion of the wearer and provide challenges from a control perspective.
Exosuits utilizing primarily soft, flexible or semi-flexible components (e.g., textiles) have been developed to address some of these issues characteristic of exoskeletons. The conformal, unobtrusive and compliant nature of many such exosuits has mitigated many of the above-identified issues associated with rigid exosuits, but in turn, raise new issues. Soft exosuits are typically not load-bearing like rigid exoskeletons, thus forces generated in the exosuit are ultimately transferred to and borne by the user's body. As such, comfort and safety considerations may limit the amount of force that can be generated to assist motion. Additionally, as soft exosuits may be worn directly against a user's skin or over clothing, comfort can be a key design consideration. Often, however, design considerations for comfort often conflict with those for maintaining efficient system stiffness for transferring loads therethrough. In particular, many comfortable textiles are prone to stretching when placed under tension. Such stretching can cause effectively bleed energy from the exosuit, making it necessary to provide larger motors and consume higher amounts of power to produce the same assistive force to the human body than if higher modulus materials were used. Additionally, stretching can cause elements of the exosuit to become misaligned and/or displaced from their intended positions on the body, potentially leading to discomfort, unnatural torquing of joints, and increased power requirements. The inherently compliant and nonlinear mechanical structure of soft exosuits can also make it difficult to accurately and reliably deliver a desired amount of force to various portions of the user's body to assist with motion. Accordingly, there is a need for a lightweight, comfortable exosuit for assistive motion configured to maintain a desired position and alignment on the body, and provide efficient load paths and transfer characteristics therethrough.
Apart from the mechanical challenges of actuating a soft exosuit, another is in delivering effective assistance given considerable variability in joint kinematics and patterns of muscle activation. Existing approaches to controlling motion assistance estimate the onset of assistance using historical data or predetermined constants, and thus fail to account for normal or unpredictable variations in the wearer's current stride. In particular, many control systems utilize historical or predetermined data from previous strides to estimate the onset of the motion to be assisted during a current stride. Other systems may be configured to apply power at predetermined, constant time offsets set to correspond with certain portions of an average person's gait cycle. This may be problematic in situations where the user's gait varies, which is often the case in real-life activity. Accordingly, there is a need for a control system configured to adapt in real-time to a user's motion and thus provide assistive power with appropriate timing and magnitude.
Another challenge is delivering effective assistance given the considerable variability in wearer kinetics due to gender, age, height, body weight, and spatial-temporal factors such as locomotive speed. Existing control systems fail to account for these variations, instead providing a one-size-fits-all magnitude of assistance that is not tailored to the particular wearer of the exosuit. Accordingly, there is a need for a control system configured to adapt the magnitude of assistance to the particular wearer of the exosuit and/or characteristics of the activity being performed.